1. Field of the Invention
The invention relates to a method and to a circuit arrangement for converting frequency modulated signals through at least one intermediate frequency into low frequency signals.
2. Description of the Prior Art
West German DE-OS No. 30 48 263 describes a radio receiver provided with a filter arrangement. The received signal is converted via one or more mixer stages into intermediate frequency signals, which are fed via intermediate frequency filters to a demodulator, in which they are converted into low frequency signals. In order to keep interference at a minimum level, the filters are constructed in a narrow-band manner. A control voltage, derived from the output voltage of the demodulator displaces the resonance frequency of the narrow-band intermediate frequency filter connected upstream of the demodulator in such a way that the particular instantaneous value of the intermediate frequency is always within the band pass range of the filter.
As the control voltage is generated after mixing and selection as a result of the reverse control, control delays occur which are essentially given by the envelope delays of the filter. This means that the control voltage for the filter and the intermediate frequency voltage are time-shifted and there is a relative movement between the filter frequency and the intermediate frequency. In the case of high frequencies, this delay leads to difficulties in the follow-up of the filter so that interference can occur.
The intent of this invention is to provide a method and a circuit arrangement for converting frequency modulated signals through at least one intermediate frequency into low frequency signals, while improving the follow-up characteristics of the filter.